A Phase 3 clinical trial assessing Merck's (NYSE:MRK) letermovir (MK-8228) for preventing clinically significant cytomegalovirus (CMV) infection in CMV-seropositive adults who have undergone an allogeneic hematopoietic stem cell transplant (HSCT) met its primary endpoint of a statistically valid percentage of patients with clinically significant CMV infection up to 24 weeks after HSCT. Full results will be submitted for presentation at a future scientific conference.

The study enrolled 540 subjects who received letermovir once daily either in an oral tablet or intravenously. Therapy was begun as early as the same day as the HSCT and no later than 28 days post-transplant and continued for ~100 days.

Letermovir is a 3,4 dihydro-quinazoline which is a new class of non-nucleoside CMV inhibitors. It inhibits viral replication by targeting the viral terminase complex. It has Orphan Drug status in the U.S., Europe and Japan and Fast Track status in the U.S.